Not Applicable
The present invention relates to cardiac treatment, and particularly relates to methods and devices for treating cardiac conditions such as atrial fibrillation.
Atrial fibrillation is a common cardiac rhythm disorder which can affect the quality of a patient""s life and may be associated with significant morbidity. Atrial fibrillation is characterized by a rapid disorganized rhythm of the upper chambers of the heart (the atria). Instead of a single wavefront of electrical activation during regular rhythm, atria fibrillation consists of multiple coexistent wavefronts with random reentry. The condition may arise following cardiac surgery, or after infection. Its etiology is varied and has even been hypothesized in some cases to have a genetic component. While medication is effective to control fibrillation in some patients, endocardial ablation or surgical intervention is often necessary for effective treatment.
Endovascular approaches may be used to create lesions using an ablation catheter to block intraatrial conduction. Surgical procedures such as Cox""s maze have been used to address the problem. This procedure creates surgical lines to compartmentalize the tissue of the cardiac wall into a plurality of regions which are each too small to support a depolarization/repolarization cycle.
The results of early clinical trials of ablation to treat atrial fibrillation indicate that in a significant proportion of patients with atrial fibrillation, the cause lies in the pulmonary veins. The pulmonary veins contain a sleeve of heart muscle in their proximal extension from the left atrium, and episodes of atrial fibrillation are often triggered by rapidly discharging foci in this region of the pulmonary veins. Such rapidly discharging foci may be located as far as several centimeters up a pulmonary vein. Catheter ablation of focal triggers in the pulmonary veins has been reported to prevent the recurrence of atrial fibrillation in some patients.
This suggests that rather than attempting to localize sparsely scattered groups of rapidly depolarizing cells, these triggers may be blocked by creating a circumferential lesion at the os of the pulmonary vein, thus simply electrically isolating the entire pulmonary vein from the atrium. Indeed, where a trigger from a venous focus is necessary to initiate or maintain fibrillation, such a circumferential lesion may be all that is required for successful ablation treatment in a significant proportion of patients.
However, clinical case reports indicate that the application of RF energy within the pulmonary veins may be associated with a risk of developing stenosis subsequent to the ablation. This stenosis can result in pulmonary hypertension, requiring a follow-up pulmonary vein balloon angioplasty or other intervention for its resolution.
Thus, treatment of atrial fibrillation in this set of patients by extracardiac ablation may require close follow up and secondary treatment to avoid complications.
It would therefore be desirable to provide a non-surgical treatment for atrial fibrillation.
It would further be desirable to provide a non-surgical treatment without stenotic complications.
This is achieved in accordance with the present invention by inserting a self-expanding stent configured to lodge in a pulmonary vein and having an exposed conductive region forming a loop. The stent is delivered via a flexibly deflectable endovascular delivery catheter, which is inserted in a femoral vein and follows a transseptal path to carry the stent in a compact form through the left atrium and deliver it to the pulmonary vein. The stent is then at least partially released or ejected from the catheter and expands into position such that the exposed conductive loop contacts the pulmonary vein around the vessel""s interior circumference. The stent remains electrically attached to the catheter, which carries an energy supply line, such as an RF cable or other energy conductor, or a cryogenic system, for supplying ablation energy or cryothermy to the stent. This line is then energized to form a lesion in that portion of the vessel contacting the exposed loop, after which the stent is detached from the catheter and remains positioned in the vein to maintain vessel patency. In alternative embodiments, the ablation potion may include a proximal loop sized and positioned to contact the posterior left atrial wall outside the os of the pulmonary vein and ablate a blocking lesion in the wall.
In one embodiment, the stent has the shape of a simple wire or ribbon helix with one or more full circumferential turns or windings of the helix exposed to operate as an ablation electrode and form the ablation lesion. The remaining turns of the helix may be covered by electrical insulation, so that the ablation energy is selectively placed in a circumferential line or band at the os. In another embodiment, the coil forms a closed loop which zig-zags around a ring-like contour such that when expanded it subtends a circumferential cylindrical band around the axis of the vessel. In yet another embodiment, the stent has a proximal coil or loop that is larger than, or expandable to be larger than, the distal portion of its body, which may be formed of coils, loops or other know stenting structures. The proximal portion lies against the endocardial surface of the posterior left atrium, while the distal portion anchors the stent within the pulmonary vein. In this embodiment the proximal portion may be configured to ablate a circumferential lesion outside the pulmonary vein, which may further reduce the risk of inducing pulmonary vein stenosis. Other known stent shapes and structures may be used, which contain, or which are augmented to contain, or which are selectively insulated so as to expose or leave exposed, a conductive loop positioned for defining a blocking lesion at the vessel entrance.
The stent may also be used to prevent or treat pulmonary vein stenosis following ablation of the pulmonary vein or adjacent atrium by any other form of ablative energy system, such as cryothermy, laser, ultrasound, microwave or rf energy treatment, among others. In that case, the proximal portion expands to a size larger than the pulmonary vein os.
The stent may be formed of a material such. as a shape memory alloy (e.g.. nitinol wire or a titanium or other such alloy), or such as a superelastic alloy. The wire or structural material of the stent may, moreover, be of light construction since it need only possess sufficient structural resilient force to counteract venous recoil and prevent stenosis.
In general, applicant contemplates that the ablation energy utilized in a stent of the present invention may take several forms. A radio-frequency signal may be applied to an exposed conductor, and optionally irrigation through the conductor or via an ancillary structure, may be provided to cool the surface, vary electrical conduction or otherwise modulate the lesion characteristics. Alternatively, with suitable stent and delivery structures, ablation may be effected by laser, ultrasound, microwave or cryothermal ablation. For clarity of exposition below, however, the illustrated structures shall be generally described and referred to simply as rf or electrical ablation structures.
Advantageously, the catheter need carry no balloon or other expansion mechanism, and does not actively effect stent expansion, so the delivery system can be quite small. It thus avoids the risk of balloon injury to the venous wall, and avoids the transient pulmonary vein occlusion that occurs with balloon delivery systems. Once deployed, however, the stent may be further expanded, or an anchor mechanism may be set, by balloon inflation if necessary. The electrical connection between catheter and stent may be effected by a fusible link, by a removable ribbon or wire attached with conductive adhesive, or by temporary capture of the stent between, or electrical contact with, conductive components of the stent delivery mechanism.
Once placed, the stent functions as a wall support in the pulmonary vein and thus may reduce wall stress and stretching that occurs, for example, in the presence of left ventricular diastolic dysfunction, mitral stenosis or regurgitation, or other conditions of left atrial hypertension. This further therapeutic support is therefore believed to contribute generally to the integrity of the vessel wall and the health of the subtended lung, and remove a potential contribution to the development of automaticity in the pulmonary vein myocytes.